Buoyancy control techniques are generally known for underwater vehicles such as autonomous underwater vehicles (AUVs), submersible remotely operated vehicles (ROVs), manned submarines, and/or other underwater vehicles. Buoyancy may be controlled by affecting the overall density of an underwater vehicle relative to the density of the water in which the underwater vehicle is submersed. Because density is a function of volume and mass, affecting the overall density of an underwater vehicle typically may be achieved by affecting one or both of the effective volume of the underwater vehicle or the effective mass of the underwater vehicle. Affecting the effective volume of the underwater vehicle may be achieved by increasing or decreasing the volume of a flexible chamber that is external to a fixed volume body of the underwater vehicle. Affecting the effective mass of the underwater vehicle may be achieved by using surrounding water to fill a tank disposed within the underwater vehicle or draining that tank into the surrounding water. In either of these approaches, pumps are used to move fluid from one location to another. The energy required to operate such pumps may be a limiting factor for missions performed by an underwater vehicle. For example, the deployment duration of an underwater vehicle may be cut short if onboard batteries need to be changed or recharged, or if fuel needs to be replenished.